1. Field of the Invention
This invention relates to a dielectric ceramic composition for use in making microwave devices, and more particularly to a microwave dielectric ceramic composition which exhibits a high specific dielectric constant .epsilon.r and a high no load value Q, and, in addition, a positive or negative temperature coefficient .eta.f of about zero can be obtained by changing the compositional ratio.
2. Related Art of the Invention
A dielectric ceramic composition utilized for ceramic capacitors for use in temperature compensation, as well as dielectric resonators for use in microwave circuits or the like has been required to have a high specific dielectric constant .epsilon.r as well as a high no load value Q, and further should obtain a positive or negative temperature coefficient .eta.f of the resonance frequency of about zero.
As such a dielectric ceramic composition, a BaO--TiO.sub.2 type, a MgO--TiO.sub.2 --CaO type, and a BaO--TiO.sub.2 --Sm.sub.2 O.sub.3 --La.sub.2 O.sub.3 type and the like have heretofore been employed. A dielectric ceramic composition of the BaO--TiO.sub.2 --Sm.sub.2 O.sub.3 --La.sub.2 O.sub.3 type is disclosed in Japanese unexamined patent publication No. 57-18007. The dielectric ceramic composition of the BaO--TiO.sub.2 --Sm.sub.2 O.sub.3 --La.sub.2 O.sub.3 type has a characteristics of a specific dielelctric constant .epsilon.r of 80 to 92, a no load value Q of 2000 to 2700 and a temperature coefficient .eta.f of the resonance frequency of +100 to -100 ppm/.degree.C. However, when a dielectric resonator or a capacitor is fabricated with these ceramic compositions, their specific dielectric constant .epsilon.r or no load value Q becomes a low value in the vicinity where its temperature coefficient .eta.f is zero (ppm/.degree.C.). Consequently, the size of a such device as dielectric resonators and the like fabricated with these materials becomes too large.